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WEI AND XU: SURVEY OF FORCE-ASSISTED ROBOTIC CELL MICROINJECTION TECHNOLOGIES 3
Fig. 2. Semiautomated adherent cell injection system (AIS 2),
1
which is
composed of microscope, motorized stage and micromanipulator, pressure
microinjector, and video camera system.
control, this injection system can achieve a high success rate
of injection. The software controls the precise injection process
and enables fast axial injection at a rate of up to 1500 cells/h.
In addition, retrieving injected cells and multiple injections
into the same cell are also achieved with this system [35].
Although some systems have already partially automated
the process, all the devices currently need extensive manual
work. Because of the participation of the operator, the quantity
of cells that can be injected in a prescribed time is limited.
This can be an issue when a plenty of cells have to be
injected or when microinjection is used to produce stable
transfected cell lines. Moreover, the skills of the operator have
a huge effect on the success rate. Another disadvantage is
the lack of method to diagnose the condition of micropipette,
such as clogging and small breakages. The drawbacks of the
individual devices result in low throughput, low success rate,
and decreased reliability of the results [9], [16].
Some researchers have devoted to improve the degree
of automation and success rate by adding force sen-
sor. For instance, Kallio and Kuncova-Kallio [16] and
Lukkari and Kallio et al. [36] have developed an impedance
sensor to detect the contact between the cell and inject
micropipette, a broken micropipette, a clogged micropipette,
an aged measurement electrode, and faulty injection solution,
as shown in Fig. 3(a). Meister et al. [37] used atomic force
microscopy (AFM) to achieve force-controlled injection of
adherent cells. Desmaele et al. [4] developed a force sensor
with planar structure to sense out-of-plane forces, and living
cells can be placed on the planar sensor, as shown in Fig. 3(b).
To conclude, the development of an automated robotic cell
injection system for single adherent cell is a very challenging
work. First, the uncertainties caused by biology require the
cell injection system with sufficient robustness. In addition,
each type of cell has its own properties and the state of cell
population changes over time, which increases the difficulty
for successful cultivation, detection, and injection of adherent
cells [16].
III. M
ICROINJECTION OF SUSPENDED CELLS
In a cell microinjection study, there are three popular sus-
pended cells in use, i.e., drosophila embryo, zebrafish oocytes,
1
http://www.ais2.com/
Fig. 3. Force sensors for adherent cell injection. (a) Impedance
sensor [16], [36]. (b) Planar force sensor [4].
and mouse oocytes. The technical details of suspended-cell
injection are presented in this section.
A. Requirement of Suspended-Cell Injection
Because of the freedom of movement of suspended cells
in the nutrient solution, the suspended cells need to be fixed
by additional equipment, such as a holding pipette or other
holding devices. This makes the injection procedure more
complicated and time-consuming. Moreover, the collision
between cells and manipulation instruments, or the motion
of cells themselves, can easily result in the failure of this
procedure. For instance, during the spermatozoon injection
into mouse embryos for vitro fertilization, the sharp and
extremely fine injection pipette and mouse embryos (about
98 µm in diameter) are very easy to be damaged [38].
Even though there is a tough requirement on suspended-cell
injection, the majority of the operations have been performed
manually [35]. However, the manual method features low
efficient, low repeatability, and low throughput, which cannot
meet the need for testing genetic materials when multiple
injection operations should be done in a certain time. On the
contrary, the robotic cell injection system can realize the
successful injection of suspended cells with high accuracy
and repeatability [39]. Therefore, the development of robotic
systems for suspended-cell injection has been the focus of lots
of research groups.
B. Robotic Microinjection System for Suspended Cells
Currently, some semiautomated or teleoperated robotic
injection systems for suspended cells are commercially avail-
able, such as the products supplied by Eppendorf
2
and
Narishige and Cellbiology Trading.
3
However, these products
need greatly skilled operators to carry out suspended-cell
injection. In the literature, Li et al. [40] have presented
a representative automated suspended-cell injection system,
as sketched in Fig. 4. The process of the automated
2
http://www.eppendorf.com
3
http://www.narishige-group.com/